1. Field of the Invention
This invention relates to precipitation polymerization of copolymers of a vinyl lactam and a polymerizable carboxylic acid, and, preferably to a process of making such copolymers having a wide compositional range, prepared in high yield, as a white powder, with effective control of the exothermic reaction, and without excessive thickening of the reaction product during the polymerization, and under reaction conditions which can provide a copolymer product over a wide range of molecular weights having low residual monomers, and which can be recovered easily to provide copolymer powders having advantageous physical properties.
2. Description of the Prior Art
Copolymers of vinyl lactams, e.g. vinyl pyrrolidone (VP) or vinyl caprolactam (VCL), and polymerizable carboxylic acids, e.g. acrylic acid (AA) or methacrylic acid (MAA), have found application in the photographic industry, as coatings, as biological membranes, in drug release systems, as preservatives, in oil recovery processes, in immunochemicals, and in cosmetic materials.
Solution polymerization and precipitation polymerization are two available methods for making these copolymers; see in U.S. Pat. Nos. 3,044,873; 3,862,915; and 4,283,384; and articles by Endo et al., in J. Makromol. Chem. 148, 205 (1971); and by Uelzmann, in J. Polymer Sci. 33, 377 (1958).
The solution polymerization process is used when both reactant monomers and the copolymer product are soluble in a reaction solvent. However, this method suffers from the following disadvantages:
(1) Desirable compositions of the copolymer may not be soluble in a selected solvent; (2) the yields of such copolymer may be low; (3) the copolymer may be colored; (4) the solvent may be a high boiling liquid which is difficult to separate from the copolymer; and (5) the solvent may be a protic liquid, e.g. water or mixtures thereof, which causes considerable hydrolysis of the vinyl lactam under acidic reaction conditions.
The precipitation polymerization method is useful when the monomers are soluble in the reaction solvent and the copolymers are insoluble in the solvent. Benzene, tetrahydrofuran, acetone and methyl ethyl ketone are known precipitation polymerization solvents. Unfortunately, these solvents have one or more of the following disadvantages:
(1) Useful copolymer compositions may not be insoluble in a selected reaction solvent, which restricts the process to a narrow copolymer compositional range; (2) the copolymer may precipitate only as a gelatinous mass which is difficult to filter; (3) low yields of polymer may be obtained; and (4) the solvent may be toxic.
Furthermore, during the precipitation polymerization process, (1) the reaction product may become too viscous to enable continued agitation; (2) the reaction exotherm may be quite difficult to control; and (3) a high solids content product may not be easy to obtain.
For these and other reasons, present solution polymerization and precipitation polymerization processes for making copolymers of a vinyl lactam and an acrylic acid have not been very successful on a commercial scale.
Accordingly, it is an object of this invention to provide an improved precipitation polymerization method of making copolymers of a vinyl lactam and a polymerizable carboxylic acid.
Other objects of the invention include one or more of the following:
(a) to provide an improved precipitation process under reaction conditions which avoids excessive thickening of the reaction product during the polymerization;
(b) to provide for effective control of the exotherm of the reaction;
(c) to form the copolymer product at a high solids content during the polymerization;
(d) to precipitate the copolymer in high yield as a fine, white powder;
(e) which powder is insoluble in the reaction solvent over the entire compositional range of the copolymer;
(f) which precipitate can be filtered and dried easily;
(g) to provide copolymers of all compositional ranges; and
(h) which copolymers are characterized by having a predetermined average molecular weight, low hygroscopicity, a high glass transition temperature, exhibiting polyelectrolyte behavior, and being soluble in an aqueous basic solution of pH 8 and insoluble in an aqueous acid solution of pH 3.
These and other objects and features of the invention will be made apparent from the following description of the invention.